Mutations of SCN4A gene cause different diseases: 2 case reports and literature review.

SCN4A encodes the Nav1.4 channel and mutations in SCN4A lead to different ionic channelopathies. In this study, one sporadic individual of periodic paralysis, one paramyotonia family and 200 normal healthy controls are enrolled. Genomic DNA was extracted from peripheral blood leukocytes, followed by polymerase chain reaction and DNA sequencing of candidate genes, including SCN4A and CACNA1S. As a result, heterozygous mutations c.2024G>A (R675Q) and c.1333G>A (V445M) of gene SCN4A were identified in the hypokalemic periodic paralysis patient and the paramyotonia congenita family respectively. Both mutations were not detected in healthy controls. Compared with reported cases, patients with mutation R675Q usually do not present hypokalemic periodic paralysis but hyperkalemic or normokalemic periodic paralysis. The mutation V445M was first reported in Chinese patients with nondystrophic myotonias. In addition, we carried out literature review by summarizing clinical features of the 2 mutations and establish the genotype-phenotype correlations to provide guidance for diagnosis.